Keyframes won't respond to 'Cycles' f-curve modifier
The Cycles f-curve modifier is working, but you have a keyframe on frame 4335 which is being included in the modifier. This means any repetitions of those keyframes are happening after frame 4335. If you zoom very far out after adding the modifier you can see that.

I presume you actually want that keyframe to be on frame 105 as that causes creates the same repeating pattern as the X Scale channel.